Edm machine head and hydraulic pressure apparatus

ABSTRACT

An electrical discharge machining device or EDM machine having a head carrying an electrode which is movable toward and away from a work piece by a hydraulically operated double acting cylinder. A control valve, combined with a servo solenoid and manually operated lever, is operable to control the flow of hydraulic fluid to the cylinder. A light responsive electrical control operates the servo solenoid in response to the size of the electrical discharge gap between the electrode and the work piece. Interposed in the fluid line to the hydraulic cylinder is a lock valve operable to lock the cylinder and fix the position of the electrode relative to the work piece. The manually controlled lever is operable to engage switches to override the lock valve control during the electrical machining and elevation of the electrode operations of the device. Hydraulic pressure is continuously supplied to the control valve from a pair of liquid storing chambers connected to the control valve with a switching valve. Fluid under pressure in either one of the chambers operates the switching valve to provide a continuous source of hydraulic fluid under pressure to the control valve. The head contains the hydraulic pressure source, control valve, EDM power supply, electric control circuit for the valve and the double acting cylinder.

United States Patent Olsson [4 1 *May 9, 1972 [7 2] Inventor: Sven O.Olsson, Edina, Minn.

[73] Assignee: Essar Corporation, Minneapolis, Minn.

[ Notice: The portion of the term of this patent subsequent to Sept. 14,1988, has been disclaimed.

[22] Filed: Dec. 8, 1970 [211 App]. No.: 96,024

Related U.S. Application Data [62] Division of Ser. No. 819,006, Apr.24, 1969, Pat. No.

52 us. or ..219/69 0, 219/69 D [51] Int. Cl. ..B23p 1/08,B23p 1/14 [58]Field of Search ..219/69 G, 69 V [56] References Cited UNITED STATESPATENTS 2,989,616 6/1961 Mironoff ..219/69 G 3,371,182 2/1968 Smith........219/69 V 3,289,029 11/1966 Webb .219/69 G X 2,485,361 10/1949 Conditet a1. ....2l9/69 V 2,730,602 1/1956 Porterfield ..219/69 V 2,762,9469/1956 Manchester ..219/69GX Primary Examiner-R. F. StaublyAttorney-Burd, Braddock & Bartz [57] ABSTRACT An electrical dischargemachining device or EDM machine having a head carrying an electrodewhich is movable toward and away from a work piece by a hydraulicallyoperated double acting cylinder. A control valve, combined with a servosolenoid and manually operated lever, is operable to control the flow ofhydraulic fluid to the cylinder. A light responsive electrical controloperates the servo solenoid in response to the size of the electricaldischarge gap. between the electrode and the work piece. lnterposed inthe fluid line to the hydraulic cylinder is a lock valve operable tolock the cylinder and fix the position of the electrode relative to thework piece. The manually controlled lever is operable to engage switchesto override the lock valve control during the electrical machining andelevation of the electrode operations of the device. Hydraulic pressureis continuously supplied to the control valve from a pair of liquidstoring chambers connected to the control valve with a switching valve.Fluid under pressure in either one of the chambers operates theswitching valve to provide a continuous source of hydraulic fluid underpressure to the control valve. The head contains the hydraulic pressuresource, control valve, EDM power supply, electric control circuit forthe valve and the double acting cylinder.

13 Claims, 6 Drawing Figures PATENTEDMM 9 1972 3,662,142

sum 2 or 4 I N VEN'I'OR. Saw 0. 01530 Jrroawsrs EDM MACHINE HEAD ANDHYDRAULIC PRESSURE APPARATUS CROSS REFERENCE TO RELATED APPLICATION Thisapplication is a division of U.S. application Ser. No. 819,006 filedApril 24, 1969, now U.S. Patent No. 3,604,884.

BACKGROUND OF THE INVENTION Electro discharge machining devices known asEDM machines have used hydraulic systems controlled with servomechanismsto regulate the spark erosion of the electrodes. The greatest efficiencyand best results are obtained in EDM machines when the electrode ismaintained in a position which insures constant sparking. Such constanceis obtained when the electrode, which represents the tool, can be movedwith very short response times and with extremely accurate feed. Thevariation in the voltage between the electrode and the work piece isused to obtain a feed of the electrode into the work piece. Themachining will be irregular when the electrode short circuits with thework piece. The electrode must be retracted to eliminate the shortcircuit before the machining can be continued. The short circuits candegenerate into arcing or weld spots which seriously damage the machinesurface of the work piece. Some prior art servomechanisms have beenequipped with a ball-type valve in the fluid discharge line operatedwith an electrodynamic coil to control and balance the fluid system forthe electrode. The variations in the machining voltage is used tocontrol the position of the ball valve to regulate the flow of fluid inthe system and thereby control the feeding of the electrode relative tothe work piece. This valve isv located in the fluid return line tocontrol fluid pressure on one side of the fluid system. Fixedrestrictors provide fluid pressure differences between opposite sides ofthe fluid system. I

The hydraulic pressure sources for these machines are separate unitslocated in the bases of the machines or adjacent the back of machines.

SUMMARY OF INVENTION Theinvention relates to an EDM device having a headcomprising frame means carrying a movable member adapted to hold anelectrode and selectively move the electrode toward and away from a workpiece. A hydraulic control system located in the head controls themovement of the movable member. The hydraulic control system has ahydraulic pressuresource coupled to a valve selectively controlled by aservomotor, as a solenoid, and a manually operated means. The servomotoris controlled in response to variations in the cutting voltage toprovide a relatively constant feeding of the electrode into the workpiece. The manual control is operative to override and cancel theservomotor to provide for rapid elevation and lowering of the electrodeand to disengage a hydraulic lock structure.

A further feature of the invention is an apparatus for supplying acontinuous source of hydraulic fluid pressure into the hydraulic systemof the electrical discharge machining device. This apparatus has a pairof storing chambers selectively subjected to pneumatic fluid underpressure. A first control operable in response to the level of hydraulicfluid in one chamber supplies pneumatic pressure selectively to thefirst chamber and the second chamber. A hydraulic fluid control valve isoperable to selectively exhaust and return hydraulic fluid to thechambers. The hydraulic fluid valve is controlled in response to thepressures of the hydraulic fluid in the chambers so that hydraulic fluidflows out of one chamber into the hydraulic system and back into theopposite chamber.

in the drawings:

FIG. 1 is a front elevational view of an EDM machine equipped with thecontrol system of the invention with part of the dielectric liquid tankbroken away to show the electrode and work piece;

FIG. 2 is an enlarged sectional view taken along line 22 of FIG. 1;

FIG. 3A is a diagrammatic view of the constant fluid pressure system tosupply fluid under pressure to the electrode control cylinder;

FIG. 3B is a diagrammatic view of the electric and fluid control systemof the invention;

FIG. 4 is an electrical diagram of the automatic depth control anddielectric liquid level control; and

FIG. 5 is a sectional view taken along line5-5 of FIG. 2.

Referring to the drawing, there is shown in FIG. 1 an electricaldischarge machining device, indicated generally at 10, having a base 11carrying a movable work table 12. A tank 13 containing a dielectricliquid 14, as kerosene or EDM oils, is supported on the table 12 formovement in the X and Y directions by crank structures (not shown).Secured to the base of tank 13 is awork piece16 of a conductivematerial, as metal.

Extended over tank 13 is a machine head or upper frame 17 carrying thecontrols and hydraulic and electrical systems. Mounted on the head 17 isa movable block 18 carrying a downwardly directed support 19. Anelongated upright electrode 21 is secured to support 19. The end of theelectrode extends below the support toward the work piece 16. A pair ofupright guide rods 22 secured to the movable block 18 project upwardlyinto the head 17 to guide the block 18 for linear up and down movement.As shown in FIG. 3B, the position of block 18 is controlled with adouble acting hydraulic cylinder 23 having a piston 24 and a piston rod26. The lower end of the piston rod 26 is secured to a center portion ofthe block 18.

Cutting power or voltage is supplied to the electrode 21 from a DC powersupply 27 electrically connected to a line 28 leading to the electrode.The electrical circuit to the power supply 27 is completed through thecutting gap 29 between the lower end of the electrode 21 and thegrounded work piece 16. The gap 29 is adjusted to provide a maximumcutting efficiency by the control system of thedevice l0, hereinafterdescribed in detail.

Hydraulic fluid under pressure is applied to the cylinder 23 through asingle hydraulic fluid supply line 31 leading to a first line 32 fordirecting the fluid to the lower or rod end of the cylinder. A secondline connected to line 33 directs hydraulic fluid to the upper or pistonend of the cylinder 23. A control valve, indicated generally at 34, isinterposed in line 33 connecting line 33a with a fluid return line 36.

As shown in FIG. 2, control valve 34 comprises a housing 37 carryingmovable spool or cylindrical member 38 slidably positioned in a portedsleeve 39. Spool 38 has an annular central recess 41 providing acommunicating passageway between the ports in the sleeve 39. Oppositeportions of the spool 39 have V-shaped slots 42 for restricting the flowof hydraulic fluid to the inlet and outlet ports of the valve. Slots 42are progressively wider and deeper in an axial direction toward therecess 41. A spring 43 acting on the spool 38 biases the spool to acentral closed position toward an electric motor or solenoid 44 operableto axiallymove the spool to control the flow of hydraulic fluid to thecylinder 23. Solenoid 44 has a movable axial core connected to the endof spool 38.

As shown in FIG. 3B, the spool member 38 has five operating positions.The first position 46 permits the flow of fluid from line 33a into line36 and blocks the return flow of fluid from the lower end of cylinder23. In this manner, the cylinder piston 24 will move upwardly in thecylinder carrying the electrode 21 away from the work piece 16. Inposition 47, a restricted flow of fluid is allowed between line 33a andreturn line 36. This moves the piston 23 upwardly at a relatively slowand controlled rate. Closed position 48 blocks the flow of fluid throughthe lines 33, 33a and 36. Position 49 permits a restricted flow of fluidthrough the valve 34 from the line 33 to the line 33a. In this manner,the piston 24 is moved downwardly at a controlled rate as the area ofthe top of the piston is greater than the area at rod side of thepiston. The effective area is that of the piston rod 26. When the spoolmember 38 is in position 49, the movement of piston 24 is in aregenerative hydraulic circuit and servo controlled in response toelectrode gap 29 condition as hereinafter described in detail. Inposition 50, unrestricted flow of fluid is allowed through line 33whereby the piston 24 moves in rapid motion downwardly, as the piston 24is in a straight regenerative hydraulic circuit, carrying the electrode21 toward the .work piece 16. Positions 47, 48, and 49 are the servoworking range 51 of the control valve 34 under the control of the servosolenoid 44.

The servo solenoid 44 is electrically controlled with a Triac controller52 connected through a variable resistor unit 53 to a light sensitivemeans 54, as a photocell, light sensitive resistor and the like. Thelight sensitive means 54 functions to vary the output signal of theTriac controller 52 and thereby control the power delivered to the servosolenoid 44. The light sensitive element 54 is aligned with a light 56,as a neon lamp, connected to the power line 28. The light sensitiveelement 54 and light 56 can be single assembly or optoelectronic device.The light 56 is connected in parallel with the circuit for the electrode21 so that when the electrode is spaced from the work piece 16 the light56 will have its greatest intensity. The variable resistor element 53 isadjusted to provide a control for the action of the servo solenoid 44.This adjustment is used to control the cutting gap 29. As the cuttinggap 29 becomes smaller, the power supplied to the light 56 will bedecreased. This decrease in light intensity is sensed by the lightsensitive element 54 to produce a change in the signals supplied to theservo solenoid 44.

As shown in FIG. 2, a manual control means, indicated generally at 58,is operative to override the operation of the solenoid 44 to move thespool 38 of the control valve 34. The manual control means 58 comprisesa rack 59 positioned on an outwardly directed rod 61 secured to themovable core of the solenoid 44. Coil springs 62 located on oppositesides of the rack 59 yieldably position the rack on the rod 61 so thatthe solenoid 44 can operate independently of the'manual control means.Located in driving engagement with the teeth of rack 59 is a segmentgear 63 secured to an end of a lever 64 mounted on a housing 67 with apivot 66. Lever 64 moves between up and down positions to control themovement of the spool 38. The lever 64 projects outwardly through anupright slot 68 in the front control panel 69. As shown in FIG. 3B, thelever 64 is moved into a down position, as shown in broken lines, toposition the spool 38 to permit the flow of hydraulic fluid to the topof cyliner 23. This moves the electrode 21 down toward the work piece16. The lever 64 is also movable to an up position to position the spool38-to connect line 33a with'the return line 36. The fluid in line 31will be supplied through line 32 to the bottomof cylinder 23 and therebyraising the electrode 21 relative to the work piece 16. When the lever64 is up the electrode 21 moves up and when the lever 64 is down theelectrode moves down.

The hydraulic cylinder 23 can be locked in any position with a lockvalve 71 located in line 32. Valve 71 is a two-position, open and closedvalve operated with a lock solenoid 72. A light 73 connected in parallelwith the solenoid is operative to show that the valve 71 is in themanually locked position. A manually operated switch 74 is interposed inelectric line 76 connecting the lock solenoid 72 to the electrode 21.Switch 74 is operative to ground the solenoid and thereby manually lockthe hydraulic cylinder 23 in any desired position. The electric powersource 77 for the lock solenoid 72 is connected to a first normallyclosed switch 78 and a second single pole, double contact switch 79connected in series in a line 81 leading from the power source 77 to thesolenoid 72. Switch 79 is normally in the position closing the line 81so that the power is directed to the lock control circuit. On thelowering of the electrode 21 toward the work piece 16, the lock solenoidwill be actuated as soon as the electrode makes contact with the workpiece-16 completing the electric circuit. At that time, the lockedsolenoid will operate the valve 71 and prevent further movement of theelectrode 21. At the same time, a light 103 will be ON to indicate thatthe cylinder 23 is in the locked position. The valve 71 will remain inthe locked position as long as the switches 78 and 79 are closed.

As shown in FIGS. 1, 3B and 4, the switches 78 and 79 are located on theback of the front panel 69 adjacent the upright slot 68. Switch 78 hasan actuator finger 78A extended across the upper pathway of the lever64. Switch 79 has an actuator 79A extended downwardly adjacent to alateral recess 82 open to the slot 68. The lateral recess 82 opens tothe mid-sec tion of the slot 68 whereby the spool 38 is located in theservo working range 51. The servo solenoid 44 has a minimum resistanceto the spring 62 coupling the rack 59 with the rod 61 when lever 64 isin recess 82.

Switch 79 is also connected to a power supply relay 98 acrossfloatswitch contact 97 (FIG. 4) and closed contacts 83C of control relay83. Switch 79 is actuated by moving the lever 64 into the lateral recess82 to trigger the power supply relay 98 toprovide the cutting power tothe electrode 21. When lever 64 is moved from recess 82, the power toelectrode is cut off. The switch 79 controls the power relay 98 so thatall cutting voltages are removed from the electrode 21 except whenactual cutting is occurring.

Referring to FIGS. 1, 3B and 4, there is shown a depth controlapparatus, indicated generally at 86, operable to terminate the powersupplied to the electrode 21 after a predetermined depth has been cutinto the work piece 16. The depth control apparatus 86 comprises asupport 87 secured to a movable portion of the block 18 so that thesupport 87 moves with the electrode 21. Support 87 may be attached toone of the guide rods 22 extended upwardly into the upper frame 17 ofthe machining device. Secured to the upper end of support 87 is a topcontact block 88 connected with a line 89 to the control relay 83. Whenthe electrical circuit to contact block 88 is complete, the relay 83 isoperable and through its own contact 83C terminates the current to relay98 and power supply to the electrode 21. Mounted on the lower portion ofsupport 87 is a dial indicator 91 having an upwardly movable actuatingrod 92 in alignment with the top contact block 88 and a ground contactblock 93. Panel 69 has an upright slot 94 for accommodating and guidingthe ground contact block 93. The ground contact block 93 is locatedrelative to electrode holding block 18 adjustably secured to the frontpanel 69 whereby the depth of the cut of the electrode 21 may beadjusted by changing the vertical position of the ground contact block93 on the front panel 69. The contact block 93 is adjusted after theelectrode 21 has been moved into contact with the top of the work piece16. ,As previously described, when the electrode 21 moves downwardlyinto physical contact with the work piece 16 the lock solenoid 72circuit is electrically actuated with the parallel connected indicatinglight 103 whereby the lock valve 71 traps the hydraulic fluid in thecylinder 23 to prevent a movement of the electrode 21.

As shown in FIG. 4, when the actuating rod 92 engages the contact block88 the circuit through the control relay 83 is complete thereby closingthe relay contacts 83A and 83B. Contacts 83A bypass the depth controlapparatus to maintain imposed condition. Contacts 83B energize anindicator light 96 which tells the operator that the finished depth hasbeen reached. The holding or imposed condition of control relay 83 isdisengaged by moving lever arm 64 out of recess 82 thus deactivatingswitch 79 and that part of the circuit arrangement which pertains to theautomatically controlled features.

The control relay 83 has the normally closed contacts 83C connected to afloat controlled switch 97 operative in response to the level of thedielectric liquid 14 in the tank 13 as safety and check before currentwould pass into power-on relay 98. When the level of the liquid 14 isabove a predeter mined level, the switch 97 connects power-on relay 98engaging cutting power to the electrode 21. A light 99 connected inparallel with the relay 98 indicates when the relay 98 is in the ONposition. When the level of the liquid 14 is low, the float controlledswitch 97 disconnects power relay 98 and power to electrode 21, butconnects the current to a second relay 101 and an indicator light 102.Relay 101 has contacts 101A which bypass the switches 78 and 79connecting the lock solenoid 72 to the power source 77. Normally closedcontacts 1018 are connected in the line with light 103 so that light 103will be OFF when relay 101 is activated. The relay 101 has additionalcontacts 101C which will close and connect solenoid 72 to ground andthereby energize solenoid 72 moving the valve 71 to the closed position.In case of failure of dielectric fluid supply, power will be turned offbut with the electrode maintained at cutting position by the lock valve71. Cutting action resumes when dielectric level is restored to safelevel.

Referring to FIGS. 2 and 3A, there is shown the hydraulic fluid supplyapparatus, indicated generally at 104, for providing a continuous supplyof hydraulic fluid, as oil, under pressure to the hydraulic fluid supplyline 31 and provide a chamber for return fluid from the return line 36.The apparatus 104 has a common support or base 106 carrying a firstupright cylinder 107 having a chamber 108 for storing hydraulic fluid109. Located adjacent to cylinder 107 is a second upright hydrauliccylinder 111 having a fluid storing chamber 112. A common flat top orlid 115 secured to the cylinders 107 and 111 closes the tops of thechambers 108 and 112. The base 106 provides a common support for thecontrol valve 34, the solenoid 44, as well as the pivot frame 67 for thelever 64. Located below base 106 and secured to the side of the controlvalve 34 is a two-position switching valve 113 connected with a line 114to the bottom of chamber 108 and a line 116 to the bottom of chamber112. The valve 113 is movable in a first position as shown by theparallel arrows to supply fluid to line 31 and direct. the return fluidfrom line 36 to the chamber 112. The valve has a second position, asindicated by the cross arrows, to direct the return fluid from line 36into the chamber 109 and feed hydraulic fluid under pressure fromchamber 109 into the supply line 31. The valve 1 13 is operated by apair of pilot cylinders 117 and 119. A line 118 connects the cylinder117 to the bottom of chamber 109. In a similar manner, a line 121connects the cylinder 119 to the bottom of chamber 112. The pressure ofthe fluid 109 in the chambers actuates the cylinders to change theoperating positions of the valve 113.

As shown in FIG. 3A, the pressure on the fluid 109 in chamber 108 hasactuated cylinder 117 to position the valve 113 as indicated by theparallel arrows. The pilot cylinders 117 and 118, being responsive tothe pressure of fluid 109 in r the chambers 108 and 112, automaticallyswitch the valve 113 to a position wherein the hydraulic fluid underpressure is always supplied to the supply line 31 and connects thereturn line 36 to the chamber for receiving the hydraulic fluid.

The pressure of the hydraulic fluid in the chambers is selectivelyestablished by the operation of a two-position valve 122 for directing asupply of air 123 selectively to lines 124 and 126 connected to the topportions of the chambers 109 and 112 respectively. The valve 122 iscontrolled by a solenoid 127 and spring 128. As shown by the parallelarrows, when the solenoid is energized the air under pressure issupplied to the top of chamber 108. Chamber 112 is exhausted to theatmosphere. When the solenoid 127 is de-energized, the spring 128 movesthe valve 122 to second position shown by the cross arrows to direct theair under pressure to the chamber 112. The chamber 108 is exhausted tothe atmosphere.

The solenoid 127 is selectively energized in response to the level ofthe hydraulic fluid 109 in the chamber 108. A level control mechanismcomprises an upper level switch 129 and a lower level switch 131positioned in a centrally located tube 132. The switches 129 and 131 areactuated in response to a magnetic force carried in a float 133positioned about the tube 131. As shown in FIG. 5, float 133encapsulates a permanent sleeve magnetic 134 operable to magneticallyactuate the switches 129 and 131. The switch 131 has an overlappedwires, leaf springs or reeds contacts 136 and 137 confined within anenclosure, as a glass tube. Switch 129 is of similar construction. Theswitch 129, normally open, is closed by the magnetic force of the magnet134 when the float 133 is raised to the top of chamber 108. Switch 131is normally closed. As shown in FIG. 5, the magnet 134 opens switch 131by spreading the contacts 136 and 137.

The switch 129 is connected in a power line 138 leading to solenoid 127.A relay 139 connected in a line between switch .129 and solenoid 127 isconnected to ground by a line 141 and the normally closed switch131.'Relay 38 has a pair of holding contacts 139A connected in parallelwith the switch'129 so that when the level of the liquid 109 in thechamber 108 drops below the switch 129, the solenoid 127 will remainenergized until the float 133 moves downwardly along the'tube 132 toactuate the lower switch 131. When switch 131 is actuated, the relayopens the contacts 139A'thereby de-energizing the solenoid 127. Thespring 128 will move the valve 122 to its second position to supplyairunder pressure to the top of the chamber 112. At this time, theliquidllevel in chamber 112 is close to the top, as the return liquidfrom line 36 has been directed by the valve 113 into the chamber 112.The application of air pressure on the liquid 109 in chamber 112 willactuate the pilot cylinder 119 so that the hydraulic fluid underpressure in chamber 112 is directed into the supply line 31.

The hydraulic fluid supply apparatus 104 provides a constant supply ofhydraulic fluid under pressure to the supply line with a minimumtransfer of fluid. The level switches 129 and 131, operating inconjunction with thefloat 133 andmagnet 134, automatically operate boththe air supply valve 122 and the switching valve 113.

The above description is directed to a preferred embodiment of theelectrical discharge machining device of the invention. Changes inmaterials, size of parts, mechanical valves and linkages, and electricalparts may be made without departing from the invention.

The embodiments of the invention in which an exclusive property orprivilegeis claimed are definedas follows:

1. An electrical discharge machine head for machining a work piececomprising: frame means, a movable member mounted on the frame meansadapted to carry an electrode and selectively move the electrode towardand away from the work piece, hydraulic cylinder means mounted on theframe means and operably connected to the movable member to move themovable member relative to the frame means, an apparatus for supplying asource of hydraulic fluid under pressure mounted on the frame means, acontrol valve mounted on the frame means for controlling the supply ofhydraulic :fluid from the apparatus to the cylinder means, therebycontrolling the movement of the movable member relative to the framemeans, and control means mounted on the frame means to actuate thecontrol valve, ,said control means having an electrically operatedcontrol operable in response to cutting voltage between the electrodeand work piece to actuate the valve and manually operated means operablyconnected to the electrically operated means, said manually operatedmeans having a member movable to a position to override the electricallyoperated control to actuate the valve and thus selectively move theelectrode toward and away from the work piece independently of theelectrically operated control, and means connecting the electricallyoperated means with the manually operated means whereby the electricallyoperated control can operate independently of the manually operatedmeans.

2. The device of claim 1 wherein: said frame means includes a supportmember, said apparatus for supplying a source of hydraulic fluid underpressure and control valve being mounted on the support member.

3. The device of claim 8 wherein: said control means for the valve ismounted on the support member.

4. The device of claim 1 wherein: said manually operated means comprisesa lever movable to control the valve independently of the electricallyoperated control.

5. The device of claim 1 wherein: the movable member comprises a blockand guide rods secured to the block, said guide rods being slidablymounted in the frame means in a direction to selectively move theelectrode toward and away from the work piece, said hydraulic cylindermeans comprising a double acting cylinder having a movable memberconnected to the block.

6. An electrical discharge machine head for machining a .work piececomprising: frame means, a movable member mounted on the frame meansadapted to carry an electrode and selectively move the electrode towardand away from the work piece, hydraulic cylinder means mounted on theframe means and operably connected to the movable member to move themovable member relative to the frame means, apparatus for supplying asource of hydraulic fluid under pressure mounted on the frame means,said apparatus having a first means having a first liquid storingchamber, a second means having a second liquid storing chamber, firstvalve means connected to pneumatic fluid supply and to upper portions ofsaid first chamber and said second chamber, said first valve meanshaving a first position to direct pneumatic fluid to said first chamberand exhaust pneumatic fluid from said second chamber, and a secondposition to exhaust pneumatic fluid from the first chamber and directpneumatic fluid to the second chamber, first control means operable toselectively locate the first valve means in the first position andsecond position, second valve means connected to hydraulic fluid inletmeans and return means and to lower portions of said first chamber andsaid second chamber, said second valve means having a first position todirect pressurized hydraulic fluid from the first chamber to the inletof the control valve and to direct hydraulic fluid from the return ofthe control valve to the second chamber and a second position to directpressurized hydraulic fluid from the second chamber to the inlet of thecontrol valve and to direct hydraulic fluid from the return of thecontrol valve to the first chamber, and second control means to operatesaid second valve, control valve means mounted on the frame means forcontrolling the supply of hydraulic fluid from the apparatus to thecylinder means thereby controlling the movement of the movable memberrelative to the frame means, and control means mounted on the framemeans to actuate the control valve means.

7. The device of claim 6 wherein: the second control means includes afirst pilot valve connected to the first chamber and a second pilotvalve connected to the second chamber, said pilot valves operable toactuate the second valve in response to the application of pressure toeither pilot valve.

8. The apparatus of claim 6 wherein: the first control means includesswitch means in response to the level of hydraulic fluid in at least onechamber to selectively operate the first valve.

9. The device of claim 6 wherein: the control means comprises anelectric control operable in response to cutting voltage between theelectrode and work piece to actuate the valve and manually operatedmeans operably connected to the valve to selectively override andde-energize the electric control means to actuate the valve and thusmove the electrode toward and away from the work piece independently ofthe electric control means.

10. The device of claim 9 wherein: the manually operated means comprisesa lever movably mounted on the frame means to control the position ofthe valve independently of the electric control means.

11. The device of claim 6 wherein: said frame means includes a supportmeans, said apparatus for supplying a source of hydraulic fluid underpressure and control valve being mounted on the support means.

12. The device of claim 6 wherein: said control means for the valve ismounted on the support means.

13. The device of claim 6 wherein: the first control means includesswitch means operable in response to the level of hydraulic fluid in atleast one chamber to selectively operate the first valve.

$22353? UNITED STATES PATENT OFFICE 4 CERTIFICATE OF CORRECTION PatentNo. 3 Dated 9 1972 Inventor(s) Sven lSSOn It is certified that errorappears in the above-identified patent and that said Letters Patent arehereby corrected as shown below:

Colomn 6, line 64, claim 8" should be -claim 2-- Column 8, line 27,"claim 6" should be -claim 11-- Signed and sealed this 19th day ofSeptember 1972.

(SEAL) Attest:

EDWARD N.FLETCHER,JR. ROBERT GOTTSCHALK Commissioner of Patents-Attesting Officer 3 UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTIQN Patent NO- Dated 9,

Inventor(s) Sven O 155011 It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

(Tolumn (5, line 64, "claim 8" should he claim 2-- Column 8, line 27,"claim 6" should he claim 11-- Signed and sealed this 19th day ofSeptember 1972.

(SEAL) Attest:

ROBERT GOTTSCHALK Commissioner of Patents EDWARD M.FLETCHER,JR.Attesting Officer

1. An electrical discharge machine head for machining a work piececomprising: frame means, a movable member mounted on the frame meansadapted to carry an electrode and selectively move the electrode towardand away from the work piece, hydraulic cylinder means mounted on theframe means and operably connected to the movable member to move themovable member relative to the frame means, an apparatus for supplying asource of hydraulic fluid under pressure mounted on the frame means, acontrol valve mounted on the frame means for controlling the supply ofhydraulic fluid from the apparatus to the cylinder means, therebycontrolling the movement of the movable member relative to the framemeans, and control means mounted on the frame means to actuate thecontrol valve, said control means having an electrically operatedcontrol operable in response to cutting voltage between the electrodeand work piece to actuate the valve and manually operated means operablyconnected to the electrically operated means, said manually operatedmeans having a member movable to a position to override the electricallyoperated control to actuate the valve and thus selectively move theelectrode toward and away from the work piece independently of theelectrically operated control, and means connecting the electricallyoperated means with the manually operated means whereby the electricallyoperated control can operate independently of the manually operatedmeans.
 2. The device of claim 1 wherein: said frame means includes asupport member, said apparatus for supplying a source of hydraulic fluidunder pressure and control valve being mounted on the support member. 3.The device of claim 8 wherein: said control means for the valve ismounted on the support member.
 4. The device of claim 1 wherein: saidmanually operated means comprises a lever movable to control the valveindependently of the electrically operated control.
 5. The device ofclaim 1 wherein: the movable member comprises a block and guide rodssecured to the block, said guide rods being slidably mounted in theframe means in a direction to selectively move the electrode toward andaway from the work piece, said hydraulic cylinder means comprising adouble acting cylinder having a movable member connected to the block.6. An electrical discharge machine head for machining a work piececomprising: frame means, a movable member mounted on the frame meansadapted to carry an electrode and selectively move the electrode towardand away from the work piece, hydraulic cylinder means mounted on theframe means and operably connected to the movable member to move themovable member relative to the frame means, apparatus for supplying asource of hydraulic fluid under pressure mounted on the frame means,said apparatus having a first means having a first liquid storingChamber, a second means having a second liquid storing chamber, firstvalve means connected to pneumatic fluid supply and to upper portions ofsaid first chamber and said second chamber, said first valve meanshaving a first position to direct pneumatic fluid to said first chamberand exhaust pneumatic fluid from said second chamber, and a secondposition to exhaust pneumatic fluid from the first chamber and directpneumatic fluid to the second chamber, first control means operable toselectively locate the first valve means in the first position andsecond position, second valve means connected to hydraulic fluid inletmeans and return means and to lower portions of said first chamber andsaid second chamber, said second valve means having a first position todirect pressurized hydraulic fluid from the first chamber to the inletof the control valve and to direct hydraulic fluid from the return ofthe control valve to the second chamber and a second position to directpressurized hydraulic fluid from the second chamber to the inlet of thecontrol valve and to direct hydraulic fluid from the return of thecontrol valve to the first chamber, and second control means to operatesaid second valve, control valve means mounted on the frame means forcontrolling the supply of hydraulic fluid from the apparatus to thecylinder means thereby controlling the movement of the movable memberrelative to the frame means, and control means mounted on the framemeans to actuate the control valve means.
 7. The device of claim 6wherein: the second control means includes a first pilot valve connectedto the first chamber and a second pilot valve connected to the secondchamber, said pilot valves operable to actuate the second valve inresponse to the application of pressure to either pilot valve.
 8. Theapparatus of claim 6 wherein: the first control means includes switchmeans in response to the level of hydraulic fluid in at least onechamber to selectively operate the first valve.
 9. The device of claim 6wherein: the control means comprises an electric control operable inresponse to cutting voltage between the electrode and work piece toactuate the valve and manually operated means operably connected to thevalve to selectively override and de-energize the electric control meansto actuate the valve and thus move the electrode toward and away fromthe work piece independently of the electric control means.
 10. Thedevice of claim 9 wherein: the manually operated means comprises a levermovably mounted on the frame means to control the position of the valveindependently of the electric control means.
 11. The device of claim 6wherein: said frame means includes a support means, said apparatus forsupplying a source of hydraulic fluid under pressure and control valvebeing mounted on the support means.
 12. The device of claim 6 wherein:said control means for the valve is mounted on the support means. 13.The device of claim 6 wherein: the first control means includes switchmeans operable in response to the level of hydraulic fluid in at leastone chamber to selectively operate the first valve.